1. Field of the Invention
The present application relates generally to systems and methods for utilizing measurements from multiple sensors on a drilling tool within a wellbore to correct for measurement errors and/or determine the position of the wellbore in relation to another wellbore.
2. Description of the Related Art
Rotary steerable drilling tools can be equipped with survey instrumentation, such as measurement while drilling (MWD) instrumentation, which provides information regarding the orientation of the survey tool, and hence, the orientation of the well at the tool location. Survey instrumentation can make use of various measured quantities such as one or more of acceleration, magnetic field, and angular rate to determine the orientation of the tool and the associated wellbore with respect to a reference vector such as the Earth's gravitational field, magnetic field, or rotation vector. The determination of such directional information at generally regular intervals along the path of the well can be combined with measurements of well depth to allow the trajectory of the well to be determined. However, measurements used in this process can be subject to errors. For example, the errors may be the result of imperfections internal to the instrumentation itself or external disturbances that can affect the output of the instrumentation and its associated sensors. Internal errors can generally be accounted for using calibration techniques and other methods. However, external errors, such as errors resulting from misalignments of the sensors within the wellbore, or errors caused by disturbances affecting the relevant reference vector (e.g., the Earth's magnetic field) can be more difficult to correct.
In addition, when a wellbore is drilled in an area in which one or more existing wellbores are present it is useful to determine the relative position of the wellbore and downhole portion of the drilling tool in relation to the existing wellbore. For example, this information can be useful to avoid collisions with existing wellbores or to drill a relief well to intercept an existing well. Furthermore, there are situations in which it is useful to drill a well alongside an existing well to implement a process known as steam assisted gravity drainage (SAGD) to facilitate the retrieval of heavy oil deposits in certain parts of the world. In this case, existing methods involve inserting equipment, such as a solenoid, into the existing wellbores. The equipment gives rise to magnetic field disturbances, which can be detected by sensors in the new well and used to determine the position of the drilling tool and wellbore in relation to the existing wellbore. Such techniques can be costly, in part because of the additional equipment involved and because such operations are time consuming.